An assembly process of a rolling bearing includes a ball insertion process of loading balls (rolling elements) between an outer ring and an inner ring. For example, in the case of a deep groove ball bearing, in the ball insertion process, the outer ring and the inner ring are arranged to be eccentric to each other on a horizontal plane, and the balls are inserted from a gap formed between an inner peripheral surface of the outer ring and an outer peripheral surface of the inner ring (for example, refer to Patent Documents 1 to 3).
In the ball insertion process, a ball insertion nozzle is arranged to face one end portion of the gap between the outer ring and the inner ring, and the necessary number of balls are inserted into a space between the inner ring and the outer ring through the ball insertion nozzle. In the below, the ball insertion process is described with reference to the drawings.
First, in a deep groove ball bearing assembly process of a conventional art, following sequences (1) to (3) are performed.
(1) An inner ring 301 and an outer ring 303 of the deep groove ball bearing are fixed to a base plate 305 with being eccentric to each other (refer to FIG. 17).
The base plate 305 has a crescentic protrusion 307 having a crescent shape, as seen from above. As shown with a dotted line in FIG. 17, a height H of the crescentic protrusion 307 from a surface of the base plate 305 is set to be substantially the same as a height of the lowest surface of a ball 309 when the ball 309 is correctly inserted between the inner ring 301 and the outer ring 303 (a height at which a center of a rolling surface coincides with a center of the ball).
On the base plate 305, the outer ring 303 is placed such that the crescentic protrusion 307 is located at an inner periphery side, and the inner ring 301 is placed at an inside of the outer ring 303 such that the crescentic protrusion 307 is located at an outer periphery side. The inner ring 301 and the outer ring 303 are arranged with the crescentic protrusion 307 being positioned therebetween, and the inner ring 301 is moved in a radially opposite direction to the crescentic protrusion 307, so that a wide gap serving as an insertion space of the ball 309 is secured above the crescentic protrusion 307.
(2) The ball is inserted into the insertion space (refer to FIG. 18A).
A ball insertion nozzle 311 is arranged just above (just above the insertion space) the crescentic protrusion 307 of the inner ring 301 and the outer ring 303 placed on the base plate 305. Then, a plurality of balls 309 accommodated in advance in the ball insertion nozzle 311 is inserted into the insertion space. The ball insertion nozzle 311 is formed therein with a passage 313 having an inner diameter substantially corresponding to one ball, and the necessary number of balls is inserted in advance in the passage 313. That is, the ball insertion nozzle 311 is arranged above the insertion space at a state where a ball row having the plurality of balls vertically stacked in the passage 313 is prepared, and the ball row is inserted at once into the insertion space.
At this time, the ball 309 having collided with an upper surface of the crescentic protrusion 307 is inserted into a gap space CS between the inner ring 301 and the outer ring 303 while colliding with a surrounding surface and a following ball and flows towards any one end portion along a circumferential direction in the gap space CS. In order to smoothly move the ball 309 inserted from the ball insertion nozzle 311 in the gap space CS between the inner ring 301 and the outer ring 303, a configuration may be adopted where the base plate 305 is tilted by a predetermined angle θ from the horizontal surface, as shown in FIG. 18B.
(3) The inner ring is moved (refer to FIG. 19).
The inner ring 301 arranged with being eccentric relative to the outer ring 303 is moved to a position at which it is concentric with the outer ring 303. A radial width W of the crescentic protrusion 307 is set to a width at which the crescentic protrusion is to exactly fit between the inner ring 301 and the outer ring 303 at a state where the inner ring 301 and the outer ring 303 are concentric with each other.